The present invention is in the field of Chemical Vapor Deposition (CVD), including Plasma Enhanced Chemical Vapor Deposition (PECVD) and related processes, and pertains more particularly to methods and apparatus for controlling flux uniformity for gas delivery.
In the field of Thin Film Technology, used extensively in manufacture of integrated circuits, requirements for thinner deposition layers, better uniformity over larger surfaces, and larger production yields have been, and are, driving forces behind emerging technologies developed by equipment manufactures. As semiconductor devices become smaller and faster, the need for greater uniformity and process control in layer thickness, uniformity, resistivity and other film properties rises dramatically.
Various technologies are well known in the art for applying thin films to substrates in manufacturing steps for integrated circuits (ICs). Among the more established technologies available for applying thin films is Chemical Vapor Deposition (CVD), which includes Plasma Enhanced Chemical Vapor Deposition (PECVD). These are flux-dependent applications requiring specific and uniform substrate temperature and precursors (chemical species) to be in a state of uniformity in the process chamber in order to produce a desired film properties on a substrate surface. These requirements become more critical as substrate size increases, and as device size decreases (i.e. line width) creating a need for more complexity in chamber design and gas flow techniques to maintain adequate uniformity.
CVD systems use a variety of known apparatus for delivering precursor gases to target substrates. Generally speaking, gas delivery schemes for CVD and PECVD processes are designed specifically for one particular application and substrate size. Therefore variations in theme of such delivery apparatus and methods will depend on the particular process parameters and size of substrates being processed in a single reactor. Prior art gas manifolds and diffusers have been manufactured from a variety of materials and are widely varied in design. For example, some gas delivery manifolds are long tubes that are either straight or helical with a plurality of small, often differently sized, gas delivery holes spaced longitudinally along the manifold. Most diffusers and showerheads are basically baffle-type structures having a plurality of holes placed in circular or spiral type arrangements on opposite facing plates or surfaces. Often the holes are contained in a series of expanding radii circles on each plate. Often such apparatus is adapted only for one type of process and cannot be used with other processes using the same CVD equipment.
One characteristic that is generally required in CVD gas delivery apparatus is that hole sizes and spacing between the holes is strictly controlled such that a uniform gas distribution or zone is maintained over a particular surface area. Uneven gas flow often results if some holes are inadvertently made too large in comparison with a mean size, or placed in wrong positions. If a larger substrate is used in a same or different chamber, then the gas delivery apparatus must often be exchanged for one that is designed and adapted for the variance in substrate size and/or chamber parameters. Improvements made to manifold and diffuser designs depend largely on empirical methods in the field resulting in numerous cases of product expenditure through batch testing.
Uniform gas delivery remains a formidable challenge in the CVD processing of substrates. If gas delivery uniformity cannot be strictly controlled, layer thickness will not be uniform. The problem progresses with increased target size and as more layers are added. Moreover, many substrates to be coated already have a complex topology introducing a requirement for uniform step coverage. PECVD in many cases has advantages over CVD in step coverage by virtue of delivering more reactive chemical precursors, energized by the plasma. However, to this date, methods for gas delivery in CVD, including PECVD type systems, have much room for improvement.
One problem with many diffusing showerhead systems relates to limited gas flow dynamics and control capability. For example, gas delivered through a typical showerhead covers a diffusion zone inside the chamber that is produced by the array of diffusion holes placed in the showerhead. If a system is designed for processing a 200-mm wafer or wafer batch, the gas diffusion apparatus associated with that system will produce a zone that is optimum for that size. If the wafer size is increased or reduced beyond the fixed zone capability of a particular showerhead, then a new diffusion apparatus must be provided to accommodate the new size. There are typically no conventions for providing more than a few zones or for alternating precursor delivery for differing size substrates in one process.
In an environment wherein different sizes of substrates are commonly processed, it is desired that diffusing methods and apparatus be more flexible such that multi-zone diffusing on differing size substrates is practical using one showerhead system. This would allow for less downtime associated with swapping equipment for varying situations, and better uniformity by combining and alternating different zones during diffusion. Prior art diffusing methods and apparatus do not meet requirements for this type of flexibility.
Another problem in this technology is that various gases of different characteristics are mixed for a particular process. There are variations in density, temperature, reactivity and the like, such that perfect uniformity in gas mixture composition and density at delivery still does not produce precise uniformity in layer deposition. In some processes an intentional non-uniformity of gas delivery will be required to produce layer uniformity.
What is clearly needed is an enhanced precursor-delivery apparatus and method that allows for a strict and combined control of gas distribution over multiple target zones in a reactor, and has several degrees of freedom in gas mixing, delivery, and uniformity control. Such a system would provide a capability for adjusting gas flow in a manner that point-of-process reaction uniformity may be achieved, providing superior film property uniformity. Such a system may be adapted to function in a wide variety of CVD and PECVD applications.
In a preferred embodiment of the present invention a showerhead diffuser apparatus for a CVD process is provided, comprising a first channel region having first plural independent radially-concentric channels and individual gas supply ports from a first side of the apparatus to individual ones of the first channels; a second channel region having second plural independent radially-concentric channels and a pattern of diffusion passages from the second channels to a second side of the apparatus; a transition region between the first channel region and the second channel region having at least one transition gas passage for communicating gas from each first channel in the first region to a corresponding second channel in the second region; and a vacuum seal interface for mounting the showerhead apparatus to a CVD reactor chamber such that the first side and supply ports face away from the reactor chamber and the second side and the patterns of diffusion passages from the second channels open into the reactor chamber.
In preferred embodiments the second side comprises a flat surface such that the diffusion passages from the second channels open into the reactor chamber on a plane. Also in preferred embodiments the vacuum seal interface comprises a flange having bolt holes and an o-ring for mounting to and sealing to a wall of the reactor chamber.
To enhance gas diffusion and mixing in embodiments of the invention the supply ports into the first channels and the transition passages from the first channels into second channels are offset in position such that no supply port is aligned with a transition passage. In preferred embodiments there are also coolant passages in the second channel region facing the inside of a reactor chamber, for protecting the showerhead apparatus from heat from within the chamber, and for impeding process film deposition on the showerhead face.
In another aspect of the invention a CVD reactor system is provided, comprising a reactor chamber having an opening for a showerhead apparatus; a support in the chamber adjacent the opening, the support for a substrate to be processed; and a showerhead diffuser apparatus for a CVD process, the showerhead having a first channel region having first plural independent radially-concentric channels and individual gas supply ports from a first side of the apparatus to individual ones of the first channels, a second channel region having second plural independent radially-concentric channels and a pattern of diffusion passages from the second channels to a second side of the apparatus, a transition region between the first channel region and the second channel region having at least one transition gas passage for communicating gas from each first channel in the first region to a corresponding second channel in the second region, and a vacuum seal interface for mounting the showerhead apparatus to a CVD reactor chamber such that the first side and supply ports face away from the reactor chamber and the second side and the patterns of diffusion passages from the second channels open into the reactor chamber. In the reactor system the second side comprises a flat surface such that the diffusion passages from the second channels open into the reactor chamber on a plane.
In another aspect of the invention a method for distributing gases to a wafer in a CVD coating process is provided, comprising steps of (a) introducing gases for the process via individual supply ports into individual ones of plural radially-concentric first channels of a first channel region of a showerhead apparatus; (b) flowing the gases from the first channels via transition passages into corresponding radially-concentric second channels in a second channel region; and (c) diffusing the gases from the second channels through diffusion passages opening through a flat surface of the showerhead apparatus parallel to and adjacent the wafer to be coated.
In yet another aspect of the invention a method for adjusting gas flux distribution over a wafer in a CVD coating operation is provided, comprising steps of (a) introducing gases for the coating operation via individual supply ports into individual ones of plural radially-concentric first channels of a first channel region of a showerhead apparatus; (b) flowing the gases from the first channels via transition passages into corresponding radially-concentric second channels in a second channel region; (c) diffusing the gases from the second channels through diffusion passages opening through a flat surface of the showerhead apparatus parallel to and adjacent the wafer to be coated; and (d) adjusting the gas flux distribution over the wafer by individually metering mass flow to individual ones of the individual supply ports to the first channels.
In the embodiments of the invention for the first time a diffuser is provided with flexibility to adjust gas distribution flux in a number of different ways, allowing a diffuser to be dialed-in to account for many gas parameters such as reactivity and the like. Various embodiments of the invention are taught in enabling detail below.